Plasticizers are incorporated into a resin (usually a plastic or elastomer) to increase the flexibility, workability, or distensibility of the resin. The largest use of plasticizers is in the production of “plasticized” or flexible polyvinyl chloride (PVC) products. Typical uses of plasticized PVC include films, sheets, tubing, coated fabrics, wire and cable insulation and jacketing, toys, flooring materials such as vinyl sheet flooring or vinyl floor tiles, adhesives, sealants, inks, and medical products such as blood bags and tubing, and the like.
Other polymer systems that use small amounts of plasticizers include polyvinyl butyral, acrylic polymers, nylon, polyolefins, polyurethanes, and certain fluoroplastics. Plasticizers can also be used with rubber (although often these materials fall under the definition of extenders for rubber rather than plasticizers). A listing of the major plasticizers and their compatibilities with different polymer systems is provided in “Plasticizers,” A. D. Godwin, in Applied Polymer Science 21st Century, edited by C. D. Craver and C. E. Carraher, Elsevier (2000); pp. 157-175.
Plasticizers can be characterized on the basis of their chemical structure. The most important chemical class of plasticizers is phthalic acid esters, which accounted for 85% worldwide of PVC plasticizer usage in 2002. However, in the recent past there has been an effort to decrease the use of phthalate esters as plasticizers in PVC, particularly in end uses where the product contacts food, such as bottle cap liners and sealants, medical and food films, or for medical examination gloves, blood bags, and IV delivery systems, flexible tubing, or for toys, and the like. For these and most other uses of plasticized polymer systems, however, a successful substitute for phthalate esters has heretofore not been found.
One such suggested substitute for phthalates are esters based on cyclohexanoic acid. In the late 1990's and early 2000's, various compositions based on cyclohexanoate, cyclohexanedioates, and cyclohexanepolyoate esters were said to be useful for a range of goods from semi-rigid to highly flexible materials. See, for instance, WO 99/32427, WO 2004/046078, WO 2003/029339, WO 2004/046078, U.S. Application No. 2006-0247461, and U.S. Pat. No. 7,297,738.
Other suggested substitutes include esters based on benzoic acid (see, for instance, U.S. Pat. No. 6,740,254, and also co-pending, commonly-assigned, U.S. Provisional Patent Application No. 61/040,480, filed Mar. 28, 2008) or polyketones, such as described in U.S. Pat. No. 6,777,514; and also co-pending, commonly-assigned, U.S. Patent Publication No. 2008/0242895, filed Mar. 28, 2008. Epoxidized soybean oil, which has much longer alkyl groups (C16 to C18) has been tried as a plasticizer, but is generally used as a PVC stabilizer. Stabilizers are used in much lower concentrations than plasticizers. Copending and commonly assigned U.S. Provisional Patent Application No. 61/203,626, filed Dec. 24, 2008, discloses triglycerides with a total carbon number of the triester groups between 20 and 25, produced by esterification of glycerol with a combination of acids derived from the hydroformylation and subsequent oxidation of C3 to C9 olefins, having excellent compatibility with a wide variety of resins.
U.S. Pat. No. 2,520,084 to Dazzi discloses plasticized vinyl chloride polymers using esters of phenyl benzoic acids and aliphatic hydrocarbon alcohols as plasticizers. Suitable esters are 2-ethylhexyl m-phenylbenzoate, the corresponding para- and ortho-phenylbenzoates, or mixtures thereof, and the various phenylbenzoates of n-hexyl, 2-methylheptyl, dodecyl, dimethylheptyl, 2-butoxyethyl, and isooctyl alcohols, and other homologous straight and branched alcohols having 8 to 14 atoms. The butoxyethyl and 2-ethylhexyl esters of phenylbenzoic acid are exemplified.
“Esters of diphenic acid and their plasticizing properties”, Kulev et al., Izvestiya Tomskogo Politekhnicheskogo Instituta (1961) 111, discloses diisoamyl diphenate, bis(2-ethylhexyl diphenate and mixed heptyl, octyl and nonyl diphenates, prepared by esterification of diphenic acid, useful as plasticizers for vinyl chloride.
“Synthesis of dialkyl diphenates and their properties”, Shioda et al., Yuki Gosei Kagaku Kyokaishi (1959), 17, discloses dialkyl diphenates of C1 to C8 alcohols, useful as plasticizers for poly(vinyl chloride) formed by converting diphenic acid to diphenic anhydride and esterifying the diphenic anhydride, necessarily resulting in 2,2′-substituted diesters of diphenic anhydride.
Other references of interest include: Clary, International Journal of Organic Chemistry, 2013, 3, 143-147; U.S. 2012/0108874 A1; and U.S. Pat. No. 5,138,022.
Thus, what is needed is a method of making a general purpose plasticizer having suitable melting or chemical and thermal stability, pour point, glass transition, increased compatibility, good performance and low temperature properties.